A spindle motor performs the function of rotating a disk to enable an optical pickup which linearly reciprocates in an optical disk drive (ODD) to read data recorded on the disk. The spindle motor is installed with a clamping device for supporting the disk mounted on a turn table or a rotor yoke.
Generally, the clamping device includes a case into which the disk is inserted, a plurality of claws integrally formed at a lateral plate of the case for supporting in such a way that a center of the disk corresponds to that of the case, a plurality of arms rotatively and linearly installed to enter the lateral plate of the case and to prevent the disk from being disengaged, and an elastic member elastically supporting the arms.
In a case the disk is inserted into the case, a front lateral upper surface of the arms is contacted by an inner lower corner portion of the disk, whereby the arms rotate in such a manner that the arms descend at a front end thereof while arms rise at a rear end thereof. In a case a rear upper surface of the arms is brought into contact with an upper plate of the case, the arms are restricted in rotation so that the arms linearly move into the lateral plate of the case.
The disk has a deviation in its inner diameter. Therefore, in a case a disk with a small inner diameter is inserted into the case, there is needed a large insertion force, while in a case a disk with a large inner diameter is inserted into the case, there is needed a smaller insertion force.
In the conventional clamping device of the spindle motor, a rotation angle of the arms is always constant, because an upper plate portion of the case contacting the rear end portion of the arms is formed with a thickness of flat even surface. The disk with a smaller inner diameter suffers from a disadvantage in that an excessive insertion force is needed in case of being inserted into the case.